Have you checked for compost sold "in bulk" (unpackaged, in a pile)? This is often times less expensive than packaged. If you need several cubic yards, they sometimes can deliver (for a fee usually) or for a small amount, you will need your own containers & a suitable way to haul it home. Some municipalities & farms have composting operations plus some garden & landscaping centers have bulk compost bins. Also check with a garden club or Extension Office in your area, they sometimes know of compost sources.

We have a similar product here for sale, 40lb bags called CLM (complete landscape mix). It's $9 a bag, cheaper if I order it in bulk. I bought a truck load, had it delivered and split it between three of us. Worked out to be less than $7 a bag.